Testing system for machine-switching circuits



Jan. 26 1926. 1,570,741

w. H. HARDEN ET A1. A

TESTING SYSTEM FOR MACHINE SWITGHING CIRCUITS Filed August 25, 1923 ya' daga 52 @HW I 7/ a/ 9/ 53 6J `Fatentecl Jan. 26, 1926.

oFF-ics.,

WILLIAM H. HAnDnNorBnooKLnN, ANnMieHAEL- A. GRAEFENECKEB, 0F. NEW

YORK, .Y-7 ASSIGN-Olis'ro- AMERICAN TEL-annoia: man 'rameaux cour-ANY, A.

CORPORATION OFyNfEXYYOR/K.

TESTING, SYSTEM :son ivt'ac,111m2-swrrcHI-lrery o'IIcUITs.

Application filed Augriist B, v'191;23. Serial No.. v659,3l7.

Zio aU w/lo'nt it 'may conccmi Y d l it knownthat we, V'ILLLAM H. Hamann. and" Mie'rinnn lA'. (lrininrniinci;En, residin at Brooklyn andv New York, in the counties of'Kings and Bronx and Stateuof New' Yorlt and New York, respectively, have vinvented 'certain lin'provements iuTesting Systems for Machine-Switching Circuits, ot Which the `following is a specification. y This invention relates to a testing method and system and hastor itsv object the provision of a method andv system for making transmission tests. upon the talking-conductors in a telephone system. l

p The invention contemplates a methodof making transmission tests on telephonelines, which Consists., in connecting the transmis sion test set and 'a calling.,T device to any trunl; to be tested controlling automatic switches to selecta predetermiijied telephone line leadingv hack to the transmission test set at the point of'origin, and holding the circuit thus established While the necessary transmission tests are made.

VThe equipment for carrying outthis method consists of a transmission itest set ofu any Well known construction. together with a 'source of currentv supply, in conjunction with. a device for controlling automatic switches, also ot any well known type, the vlast 'of the train 'of switches, When set, se-l lecting a predetermined pair of. conductors Whieli' lead back to the transmission testingr set. ln making transmission tests between. offices, the said pair of conductors are con-.

`nested to a pair of trunk conductors Which 'normally terminate in a regular incoming selector, these trunk conductors terminating inthe transmission test set.

Figure l represents this invention applied Vto make transmission tests between two'` oliices ina full mechanical step-hy-step systeni.

lfig. 2 represents the invention applied to make transmission tests on a connector Iswitch in a l'ull-mechanical step-by-step sys@ tem.

Fig. 3 represents. the invention applied to make transmission .tests between ameclianiT `caloiee and idistant manual office.

leferringiioxv morel particularly to Fig. '1, Q59 represents outgoing trunk repeater circuit at oliice A, connected by Way of cable` conductors .70'. and 731. to an incoming-se lector 59, of the wellrlmownStrowger type.

at Office Similarly, 8 9 represents a secdnd; trunk, repeater circuit at 'ofiee A, ordi'- narjly connectedby Wayof conductors 8G anjd'l 8T to another incoming selector 99, at

olic'eB, The test linTL of the connector 79'conneeteol',` t'o the' terminals l82' andA of' the connector multiple .bank .is extended hy Wayjo'f'the conductors 92' and 93to the ter# minalls and 77. l The leads vvhichy ordinarily connect', conductors 86'v andrSV to terminals 28 andi29jof the selector 99 a'reconnected to terminals 7 6 and 77 While the transmission tests are inprogress,l so thatV the test line TL isanow extended by means ofjtherleads 92.y and 93, cross-Wiring 56,' and yclallole conductorsv and?. 87 `to the trunk re'- peater. circuitSQ' at officev A.` Thus, Whene'ver the test line TLisfcalled by. operatingtheV dial` D of; the dialing board DB 1n ol'lice A, it is evident that a circuit Will be established from the transmission measuringt set TMS v vay ofjthe repeater 49 in office A, conductors 7 0 and 71, selectors 59"y and 69connector 79', test line TL, (all in oliicefB), 'condueto'rss86` and 87, repeatery 89 in office A, y'to the transmission measuring set' TMS, The apparatus shown in Fig, l for purposes of illustration, shows one meth@ odfo't accomplishing this obj ect and Will non7 be described in greater. detail. y n

,Assuming that theywiring of the test line TL of,y connector 79 `in office B has been eX- tende-dy in the manner previously described and thatA the, transmission measuring set TMS anddialing board DB have been connected to the trnnk repeatersflt) and 89 at the, jacks" J and. J? by means' .Oflthe plugs 96' and 97l and"theirr associated cords., the apparatus' Will then biearranged asshown at A. Eig, 1.-; olii'ce B, the key K ,of the dialing boa-rd DB", ispoperatfedfto position 3 8 closingcircuit to operaterclay t8` as follows: battery, upper wfnde of rel-ay 48, 66.', 50,41., 39 4.6,; 4a 42,

37. 3'5, 51, 66 .to ground' at` they lower Winding` To dial'- the test line vTL im is merely indicated by brushes 80 and 81. It may be of the type shown and described in detail in Patent No. 1,176,269, issued March 21, 1916, to A. H. Blessing. When the dial D is moved on normal and released, retarc ation coil 46 is short circuited at 44 and and the circuit to operate relay 48 previously traced, is intermittently opened at 42 and 43 of the dial D. Each time this circuit is opened at 42 and 43, relay 48 releases and opens at 48 and 49 the circuit through the impulse relay of the incoming selector 59. It will, of course, be understood thatl the relays 58 and 68 are not. bridged across the talking conductors during the period relay 48 is making and breaking the impulse circuit, but that this bridge is opener during that period by a slow relay as shown and described in detail in said patent. The selector 59 functions in the manner well known in the art and selects an idle trunk in the proper level, which we will as sume to be the selector 69. This selector may be of the type shown and described in said patent. When the dial D is again moved off normal and released, relay 48 again opens and closes contacts 48 and 49 to interrupt the circuit through the impulse relay (not shown) in selector 69, causing selector' 69 to function and hunt for an idle connector in the proper level which we will assume to be the connector 79. This connector may be of the type shown in said patent. The dial D is again moved off normal and released as before and as it returns to normal the circuit through the dial D is intermittently opened at contacts 42 and 43, again intermittently operating relay 48. Relay 48 is turn operates relay 78 which causes the brushes 72 and 73 of the connector 79 to step to the proper level. 1N hen the final digit is dialled, the connector 79 rotates to the terminals of the desired line, which we will assume to be the test line TL, and machine ringing is applied to the line. The key K is now operated to position 32, substituting the retardation coil 47 for the retardation coil 46 upon the repeater circuit 49, thus preventing the connector 79 from releasing. lfVith the key K operated to position 32, the retardation coil 46 is connected to the repeater' circuit 89 by way of the oon-- tacts 33, 34, 30 and 31 of the key K. A bridge is now connected across the conductors 86 and 87 in a manner not shown, causing the machine ringing current supplied from the connector 79 to be removed from the test line TL in a manner well known in the art. .A circuit is now established to the transmission measuring set TMS as follows: contact 27 of the circuit closing key CCK, 19, 18, 23, 7, 6, 25, 50, 66', 60, 70, 80, 90, 52, 62, 72, e2, 92, 76, s6, 5i, 6i, 74.-, si, 2o, 2, i. 1i, i2, is, 10, 9,21, 85, 75, 65, 55, e7, 77, 93, 83, 73, 63, 53, 91, 81, 71, 61, 66, 51, 24, 5, 4, 22,

to contact 26 of the circuit closing key CCK. It will be observed that the retardation coils 46 and 47 and the following relays or groups of relays are bridged across this circuit 48, 58 and 68, 78, 88, 98 and 57, and 67. The retardation coils 46 and 47 are so arranged as to offer a resistance to direct current suliiciently low to insure the holding of the circuit being tested, while the impedance to alternating current at frequencies ordinarily used in testing is suiciently high to introduce a negligible transmission loss.

The source of alternating current 16 is connected over an obvious circuit including windings 14 and 15 of the transformer T. Hence when contacts 26 and 27 of the circuit closino' key CCK are closed, the circuit previously traced, including windings 18 and 19 of the transformer T, is completed and alternating current is connected over the circuit previously traced to the AC ammeter 13, which will give a certain reading.

Vfhen the Calibrating key CK is operated, and the circuit closing key CCK is closed, the windings 18 and 19 of transformer T are connected by way of the contacts 4, 3, 8 and 7 of the Calibrating key CK to the AC aninietcr 13 and variable resistance 11. Vith all of resistance 11 in the circuit, a certain deflection will be obtained on the AC ammetcr 13 and this deflection hereinafter referred to as the constant reading" vill be noted by the tester. The oalibratingi key Gli is now released and the circuit over the lines under test previously traced, is reestabliS-Lhed, and another reading will be obtained. The amount of resistance in the cir cuit new reduced by varying the variable resistance 11 of the transmission measuring set 'lin/1S until the constant reading7 again obtained. The loss in any desired unit of transn ission of the circuit under test may now be read directly from the scale of the resistance 11. The transmission loss of the test line TL, conductors 92 and 93, cable conductors 86 and 87, and the trunk rc peater 89, has previously been determined. hence by subtracting this loss from the total loss indicated on the scale of the resistance.` the trans Jion loss and the balance of the network be detern'iined. lf the loss thus deternined is not within the proper limits, the tester knovs that the transmission characteristics of the circuit are defective. Dy eliminating the outgoing trunk repeater 49 or the connector 79, or both, frein the circuit, a new reading can be obtained which, when resistance 11 is varied as'be fore, will indicate the transmission loss in the balance of the circuit. By eliminating any part of the network, for example, the outgoing trunk repeater 49 or the connector 79 from the circuit and substituting trim.- conductors of known resistance therefor the transi'nission loss for the balance of; the nctwork may be completed. It the resulting loss is within the proper limits, t-he tester knows that the particular network or "piece of apparatus eliminated is defective and proceeds to era-mine the defective apparatus in detail in order to remove the cause oli. thedefect. Ordinarily, when the tester encounters a defective circuit, he will make a memorandum threeot land then proceed to test the balanceot'the remaining circuits in the Vgroup before attempting to locate the nature of the troublefin the defective circuit.

`When the tests on the circuit including 19, 59, G9, and 79 are completed, the circuit closing key CCK is released, removing rthe altern-ating current from 'the line. The plug 96 is now removed from the test jack l and inserted in a similar test jack associated with another outgoing trunk repeater circuit and the tests are then repeated.

rFransmission measuring 'tests may be inane on any'switch or series 'of switches in a, particular otlice 'by arranging the circuit in the manner shown in Fig'. 2, where for convenience the circuit 'is 'shown arranged lior a transmission measuring test on the transmission network of a connector circuit. rl`l1e transmission 'measuring set TMS2 and the dialing board 'DB2 are similar in every respect vto the transmission Vmeasuring set and dialing board shown in Fig. l. The plugs 296 and 297 are in this case connected to the jacks 286 and 287, respectively, in the manner shown in Fig. 2. The jack 287 is asscciated with a test line TL2 which is reached by dialing the yproper' vnumber oi digits, depending ugon the number of switches in the series. In accordance with the` arrangement shown in Fig. 2, it would be necessary to'dial two digits to establish a connection between the connector circuit shown and the test line T112.

Fig. 3'shows a method followed in conduct-ing transmissionfnieasuring tests on the circuits Vfrom a step-b v-step mechanical oilice A. to a manual office C.

ln this case, the-plugs 396and 397 are inserted inthe jacks 386 and 387, respectively, oi." thc'trunks 388 and 389 with lwhiclithey are associated. The transmission'measuring @IMSS andthe dialing board DB3 Vare vsimilar in all respects to the transmission y measuring set VTMS and dialing Vboard DB in l. The test lines TLS and Tlf appear in the multiple before the Aoperator at the call indicator `position in the ymanual oliice C and are asiigned numbers -in the regular sii-bscribefs multiple i'nt'he 'usual nianner. The key K (Fig, l) is operated to the pesition 38 and the number of the test line TLS (Fig. 3) is dialled and the impulses transmitted over the conductors 330 and 331 to a call indicator' temporarily associated witlrthe circuit 398at otlice C, which causes the number of the .testline TLB to -be displayed betorethe operator at oilice C. Call indicator circuits are well known and therelore need not be shown. The call indicator may b'e of the type Vdescribed on pages 3&1 to 343 ot 4Smith and Campbells book on Automatic Telephony, 2nd edition. The plug 368 is `thereu'laon inserted in the jack 378 associated with lthe test line TLS, which causes the call indicator to restore in the wellknown manner. `The key K (Fig. l) is :now switchedto thel position marked 32., thus connecting the retardation coil 47 (Fig. l) across the'trunk-SSS (Fig. 3) to prevent the 'operator at oliice C from receiving the disconnect signal due to the release of supervisory '334'. The contacts 42 and 43 of the dial D (Fig. l) will now be connected in series with'the circuit 389 at office A (Fig. 3) andthe number ot the test line TL* may now :be dialled and the number of that line 'displayed on a call indicator temporarily associated with ythe circuit 399 Vat otlice C.

The plug 369 is thereupon inserted in the jack 379 of the test line TLt. The test lines TL3 and TL1 are connected together in the manner 'shown in Fig. 3. Hence with `the plugs 368 and 369 inserted in the jacks 378 and "379, the machineringing current "on circuits 298 and 399 will be 'removed from the circuit iin a manner rw-ell `known in the art land a circuit will be closed as follows 'from the transmissionmeasuring set TMS5, 301, 311,396, 321,331, 315, 305, sa aac, ses, 310, 300,- to the sending circuit oll `the transmission measuring set TMS3. It will be observed that this circuit is in .inductive relation 'with a circuit as follows: winding 306 oi the repeating coil RC in the trunk "398, e210, e, sco, 35i-3, 3213, esc, ssc, '326, 352,361,351, 341,329,316, to 305. It will be noted that/this circuit is also in inductive relation with the transmission receiving' set circuit as follows: winding of the repeating coil RC1 in the trunk 399, 335, 333, 323, 371, 381, transmission receiving' circuit TMSE', 380, 370, 322. 332, to 325. It will be observed that. relays 309, 318 and 319, and 334; are connected in bridge with the circuit 388, and relays 359, 348 and 349, and 337 in bridge with the circuit 389. Hence, when the alternating current from the transmission'measuring` set'rlB/IS3 is applied to the trunk 388, it will be inductively reproduced in the intermediate circuits 398 and-399 and finally reproduced in the circuit 389 and transmission receiving circuit of the transmission measuring set TMS'. Theloss sustained may be determined in a manner similar to that described in connection'witli Fig. l. Then the .necessary tests are completed,

'the plug'396 is removed from the jack lul) retained however' it desired, until all other trunks in the group have been tested, when the circuits may be restored to normal by removing the plugs 396 and 397 from the jacks associated with the lines under test.

lllhile the method of measuring transmission losses in telephone lines has, for purposes ot illustration, been shown in connection with the stcp-by-step machine switching telephone system, it is not so limited but the general method ot determining transmission losses shown herein, may be used in connection with any other testing or transmission testing system in the same general manner.

Thatis claimed is:

l. Method of establishing a transmission testing circuit which consists in connecting a transmission testing set to separated points in any circuit to be tested and completing a testing loop by controlling automatic selector switches to interconnect the parts ot the circuit to which the set is connected and in holding the circuit thus established while the tests are made.

2. Method of establishinga transmission testing circuit which consists in connecting a source ot current supply, a transmission testing set and a calling device to a circuit leading to a mechanical oiiice, controlling automatic switches thereat to build up a connection to a circuit which leads back to the transmission testing set in the originating office, and in holding the loop circuit thus established until the transmission tests are made.

3. Method of establishing a transmission testing circuit which consists in connecting a source or current supply, a transmission test set and an impulse sender t-o a circuit leading to a step-by-step mechanical oflice, controlling automatic switches thereat to provide a loop circuit bach over a predetermined line whose number corresponds to the number dialled to the transmission testing set, and in holding the loop circuit thus established while the transmission tests are made.

4.1. A method oi establishingl a transn'iission testing circuit which consists in connecting a source ot current supply, a transmi on testing` set` and calling device to a circuit leading to a mechanical otiice, controlling automatic switches tl'iereat to build up a connection to a circuit which leads baci-z to the transmission testing?` in the originating ollice, closing` the loop circuit to be tested. and in holding the loop circuit thus established, until the transmission tests are completed,

5. A method oi establishing a transmission testing circuit which consists in connecting a source ot current supply a transmission test set, and an impulse sender to a circuit leading to a step-by-step mechanical oliice, controlling automatic switches thereat to provide a circuit lack over a predetermined trunl; whose number corresponds to the number dialled to the transmission testing set, closing the loop circuit to be tested, and in holding the loop circuit thus established, while the transmission tests are completed.

6. lin a testing system for testing the transmission characteristics of automatically connected telephone talking circuits, means for connecting a transmission testing set to separated points in any circuit to be tested, means to control automatic switches to complete a testing loop tor interconnecting the parts of the circuit to which said set is connected and means to hold the circuit thus established while the tests are made.

7. ln a testing system, a source of current supply, a transmission testing set, means for connecting said source of current supply to said testing set, a plurality ot' sets ot' conductors, means for connecting said testing set to any predetermined set ot conductors, another set ot conductors, means for connecting said testing set to the last mentioned set ot conductors, means for connecting said predetermined set of conductors to said last mentioned set of conductors, a circuit including the source ot current supply, a variable resistance, the current responsive device., and a key orP said testing set, for obtaining a reading of the transmission chan acteristics or said circuit by Ymeans or". said current responsive device, a second circuit including the elements aforesaid and said predetermined, and last mentioned, sets ot conductors, and means `tor varying said resistance, to produce the reading first obtained.

8. In a multi-office testing system, a source of current supply, a calling device, a lirst office, a second ollice, a plurality of sets of conductors between said first otlice and said second otlices, means for connecting said source of current and said calling device to any predetermined set of conduct-ors at said lirst cthce, another set oi conductors between said lirst and second ollices, a pair ot conductors in said second ol'lice having a distinguishing code number, means in said second office for connecting said secondly mentioned set of conductors between said first and second olli/ces with said code numbered conductors in said second otlicc, automatic apparatus in said second oilice associative with said predetermined set ot conductors responsive to said calling` device tor differentiating between said code numbered conductors and any other conductors terminating in said second oltice, a device respon- -sive to current at said first oilice, means in said first oflice for connecting said current responsive device to said Secondly mentioned set oit conductors to said second oflice, and a circuit including said source of mman current supply, said predetermined,msaid secondly ymentioned and said code numbered conductors, and said current responsive device.

9. ina testing system, a source or' current supply, a. calling device, a plurality or sets of conductors, automatic switchingapparaf tus responsive to said calling device, means for connecting said source of current supply and ysaid callingdevice to any predetermined set oiconductors, a second set of conductors multipled before and accessible to thevlast switch in the train of switching apparatus, a third set of conductors, means for ,connecting said `second to said third set oi conductors, ya deflectable indicating device responsive to varying transmission characteristics, means for connecting said third set or' conductors to said current responsivedevice, and a circuit including said source of current supply, said predetermined, second, and third, sets of conductors, said switching apparatus, and said current responsive device. v

l0. in a transmission measuring system, a source of alternating current supply,"a plurality of sets otconductors, means for connecting said source ot current to any predetermined set of conductors, another set oi conductors, a deliectable indicating device responsive to alterna-ting current, means for connecting said current responsive device to said secondly mentioned set of conductors, means to control automatic switcihes for connecting said predetermined set or conductors to the secondly mentioned set of conductors, and a circuit including said source of alternating current supply, said predetermined and secondly mentioned lsets oi' conductors and said current responsive device. Y

il. ln a multi-oilice transmission measuring system, a source 01"' alternating current supply, a calling device, a iirst oliice, a sec- ,ondotica a. plurality otsets of conductors between said first oiice and said second oftice, means for connecting said source o current supply and said calling V device to any predetermined set of .conductors atsaid first otticm another set of conductors between said tirstaridi second oiiices, a set of conductors in saidfsecond oi'iice having a distinguishing code number, means in said second oliice for connecting' said secondly mentioned set of conductors between said iirst and second of tice with said code numbered conductors in said jsecond oiice, automatic apparatus in saidsecond oliice associative with said first mentioned predetermined setof conductors responsive to said calling device for differentiating between said code numbered conductorsand any other conductors terminating in saidsecondofice, means for connectingrsaidfirst mentioned predetermined set pt'con'ductors toasaid code numbered cond uctors, a device responsive to alternating current, means lin said irst oliice vfor connecting said current responsive device to said secondlymentioned set of conductors to said second office, and a circuit-,including said lsource of alternating current supply, said predetermined, secondly mentioned, and code numbered conductors and said current iesponsivedevicc,

, l12in a. transmission Amezusuring system, a source of v alternating current supply, a calling device, a yplurality of sets of conductors each set associated with automatic switching apparatus responsive to said calling device, means for connecting saidsource of alternating `current supply and said calling `device to any .predetermined set of conductors,` a second set oipconductors multipled before and accessible to the last switch in the train of vswitching apparatus, a third set of conductors, means for connecting said` second to said lthird s et of conductors, a vdevice responsive to valternating current, means for connecting said third set of conductors tosaid current responsive device, and a circuit including said` source of alternating current supply, said predetermined, second, and third sets of conductors, said switching apparatus. and said current responsive device.A y y Y .13. In a telephonetransmission measuring system, a source of alternating current supply, a plurality telephone linesforming' a group, means for connecting said source of alternatingcurrent to any-predetermined telephone line in said group, ai deflectable indicating device responsive to alternating current, means for connecting said current responsive ldevice to a second predetermined line in the group aoresaid,"means to control automatic switches for connecting said iirst and second predetermined lines together, anda circuit including said source of alternating current, said rst and second mentioned Atelephone lines and.' said' current responsive` device.

14. In a multi-office telephone transmission measuring system, a source of alternating current supply, a calling device, a first ndice, Va second oiiice, a plurality of telephone lines forming a group between said rst and second oifices, means for connecting said source Ofalternating current and said calling device to any predetermined tele-v phone line in the group at said lirst oiiice, a second predetermined telephone line in said group, a test line in said second office having a distinguishingcode number, means in said second othce for connecting said second predetermined telephone line to said test line, automatic apparatus in said second oiicey associative with said first mentioned predetermined telephone line respon- `sive tosaid calling device for dierentiatingbetween said ltest lineand any other line lll) terminating in said second office, a device responsive to alternating current, means in said first office for connecting said current responsive device t0 said secondly mentioned predetermined telephone line, and a circuit including said source of alternating current supply, said first and second mentioned predetermined telephone lines, said test line and said current responsive device.

15. In a telephone transmission measuring system, a source of alternating current supply, a calling device, a plurality of telephone lines forming a group, each line equipped with automatic switching apparatus responsive to said calling device, means for connecting said source of current supply and said calling device to any predetermined telephone line in said group, a test line multipled before and accessible to the last switch in the train of switching apparatus, a second predetermined telephone line in the group aforesaid, means for connecting said test line to said second predetermined telephone line, a device responsive to alternating current, means for connecting said second predetermined line to said current responsive device, and a circuit including said source of alternating current supply, said predetermined first, and second, telephone lines, said switching apparatus, said test line, and said current responsive device.

16. In a telephone transmission measuring system, a source of current supply, a transmission testing set, means for connecting the source of current supply to the testing set, a plurality of telephone lines forming a group, means for connecting said testing set to any predetermined telephone line in said group, a second predetermined telephone line in the group aforesaid, means for connecting said first mentioned predetermined telephone line to said secondly mentioned telephone line, means 'for connecting said secondly lmentioned telephoney line to the testing set, a circuit including the source of current supply, a variable resistance, the current responsive device, and a key of said testing set for obtaining' a reading on said circuit by means of said current responsive device, a second circuit including the elements aforesaid, and said predetermined and last mentioned telephone lines, and means for varying said resistance to produce the reading first obtained.

17. In a. multi-office transmission measuring system, a source of current supply, a transmission testing set, means for connecting the source of current supply to the testing set, a calling device, a first office, a second office, a plurality of telephone lines forming a group between said first and second offices, means for connecting said testing set and the calling device to a predetermined line in the group at the first office, a second predetermined line in said group, a test line in said second oce having a distinguishing code number, means in said second office for connecting said secondly mentioned predetermined telephone line to said test line, automatic apparatus in the second office associative with said first mentioned predetermined telephone line responsive to said calling device for differentiating between said test line and any other line terminating in said second office, means in said first office for connecting the testing set to said secondly mentioned predetermined telephone line, a circuit including the source of current supply, a variable resistance, the current responsive device and a key of said testing set for obtaining a reading on said circuit by means of said current responsive device, a second circuit including the elements aforesaid, said first mentioned, said secondly mentioned predetermined telephone lines and said test line, and means for varying said resistance to produce the reading first obtained.

18. In a multi-oce transmission measuring system, a source of alternating current supply, a transmission testing set, means for connecting the source of alternating current supply to the testing set, a calling device, a first office, a second office, a plurality of telephone lines forming a group between said first and second offices, means for connecting the testing set and the calling device to a predetermined telephone line in the group at the first office, a second predetermined line in said group, a test line in said second office having a distinguishing` code number, means in said second office for connecting the second predetermined telephone line to said test line, automatic apparatus in the second office associative with said first mentioned predetermined telephone line, responsive. to said calling device, for differentiating between said test line and any other line tern'iinating in said Second office, means in said first office for connecting the testing set to said secondly mentioned predetermined telephone line, a circuit including a variable resistance, the current responsive device and a key of said testing set, in inductive relation with a circuit includlng said source of alternating current supply, for obtaining` a reading on the first mentioned circuit by means of said current responsive device, a third circuit, in inductive relation with the circuit including said source of alternating current supply, comprising the elements aforesaid, said first, and secondly mentioned predetermined telephone lines, and said test line, and means for varying said resistance to produce the reading. first obtained.

19. In a multi-office transmission measuring system, a source of alternating current supply, a transmission testing set, means for connecting the source of alternating current supply to the ltesting' set, a calling device,

first oiiice, a second office, a plurality of telephone lines forming a group between saidfirst and second offices, means for connecting the testing set and the calling device to a predetermined telephone line in the group at the first o'tlice, a second predetermined line in said group, a test line in the second office having a. distinguishing code number, means in the second ofii-ce for connecting said second predetermined telephone line to said test line, automatic appara-tus in the second office associative with both said first and second mentioned predetermined telephone lines responsive to said calling device for differentiating between said test line and any other line terminating in said second office, means in said first office for connecting the testing set to said secondly mentioned predetermined line, a circuit including a variable resistance, the current responsive device and a key of said testing set, in inductive relation with a circuit including the source of alternating current supply for obtaining a reading;` on the first mentioned circuit by means of said current responsive device, a third circuit, ininductive relation with the circuit including said source of alternating current supply', comprising the elements aforesaid, said first and secondly mentioned predetermined telephone lines, and said test line, and means for varying said resistance to produce the read ing first obtained.

20. In a. telephone transmission measuring system, a source of alternating current supply, a transmission testing set, a calling device, a plurality of telephone lines forming a group, each line equipped with automatic switching apparatus responsive to said calling device, means for connecting said source of alternating` current supply to the testing set, means forl connecting the testing set and the calling device to any predetermined telephone line in said group, a test line multipled before and accessible to the last switch in the train of switching apparatus, a second predetermined telephone line in the group aforesaid` means for connecting said test line to said secondly mentioned predetermined telephone line, means for connecting said secondly mentioned predetermined telephone line to said testing set, a circuit including a variable resistance, current responsive device, and al key ofl said testing set, yin inductive relation with a second circuit including said source of alter'- nating current supply, for obtaining a reading on the first mentioned circuit by means of said current responsive device, a third circuit in inductive relation with the circuit including said source of alternating current supply, comprising` the elements aforesaid, said first and secondly mentioned predeter mined telephone lines,l and said test line,

and means lfor lvarying said resistance to produce the reading first obtained.k

21. The method of testing` the characteristics of transmission lines which consists in taking' one of said lines and a line whose transmission loss is known, connecting the transmission ymeasuring device to these lines, establishing a connection at a distant point over the line to be tested in accordance with its normal mode'of operation to the line whose loss is known, manipulating the transmission testing devicel to determine the transmission loss of the combination, releasing the line tested, mathematically determining the transmission loss of the line tested, and deducing therefrom its transmission characteristics.

22. The method of testing the characteristics of transmission lines which consists in taking one of said lines and a line whose transmission loss is known, connecting the transmission measuring device to these lines, establishing a connection at a distant point over the line to be tested in accordance with its normal mode of operation to the line whose loss is known, manipulating the transmission testing device to determinethe transmission loss of t-he combination, releasing the line tested, mathematically determining the transmission loss of the line tested, and of deducing therefrom its transmission characteristics, all steps in the method being conducted without interfering with the normal use of subscribers lines.

23. The method of testing the characteristics of transmission lines which consists in taking one of said lines and a line whose transmission loss is known, of assigning a distinguishing designation to the linevof known loss, connecting the transmission measuring device to these lines, establishing a connection at a distant point over theline to be tested in accordance with its normal mode of operation to the line whose loss is known, manipulating the transmission testing device to determine the transmission loss of the combination, releasing the line tested, mathematically determining the transmission loss of theline tested, and deducing therefrom its transmission characteristics, all steps in the method being conducted without interfering with the normal use of subscribers lines.

24. The method of testing the characteristics of transmission lines which consists in taking one of said lines and a line whose transmission loss is known, of assigning a distinguishing designation to the line of known loss, connecting the transmission measuring device to these lines, transmitting signals corresponding to a distinguishing designation of the line of known loss over the line tested whereby a connection is established at the distant point with t-he line Whose loss is known, manipulating the transmission testing device to determine the transmission loss Vof the combination, releasing the line tested, mathematically determining the transmission loss of the line Jtested, and dednoing theieiirom its transmission cha-racteristics, all steps in the method being Conducted Without interfering` with the normal use of subscribe1"s lines.

ln testimony whereof, We have signed ouil0 names to this specification this 28rd day or August, 1923.

lTlLLL/lv H. HARDEN. VHCHAEL A. GRAEFENECKER. 

